The objective of this project is to aid in the development of successful dental restorative materials by evaluating a number of material properties and characteristics of newly developed composite resin. The general hypothesis is that low shrinkage nanofiller and conventional filler composites will have a balance of mechanical and physical properties superior to a clinically successful, commercially available reference composite. As such, similar properties of a conventional unfilled model system (Bis-GMA based), a conventional filled model system (glass or silica filler in a bis-GMA based resin), and a commercially available reference composite will also be determined. To test the general hypothesis, three specific aims are proposed. The transverse strength, fracture toughness, shrinkage and morphological characteristics of the restorative composite resins will be measure in specific aim 1. Aim 2 will measure selected mechanical (compressive strength, elastic modulus, surface roughness and wear resistance) and physical properties (depth of cure, water sorption, coefficient of thermal expansion, rheology, radiopacity, and color stability) of restorative composite resins to identify favorable resin composite formulations. The shear bond strength of the restorative composite resin, in the presence and absence of OP-1 tertiary dentin-stimulating treatment, using a commercially available dentin bonding agent will be measured in Aim 3. In aim 3, Scotchbond Multipurpose will be used as the dentin bonding agent used. It is known that a series of materials tests for prototype resin composites will play a significant role in guiding the evolution, refinement and eventual scale up of the materials used to develop a novel restorative system. Thus, the outcome of these comprehensive tests will allow newly developed resin composites to be compared to a clinically successful restorative material. It is also through these comprehensive tests that the ultimate formulation for model resin composites will be selected for eventual evaluation in the oral environment.